Phase-contrast magnetic resonance image data acquisition with velocity-encoding provides cardiovascular flow visualization and quantification of severity of stenosis by evaluating a peak blood flow velocity within a core of a post-stenotic jet. However, this method often underestimates peak velocity of flow jets due in part to reliance on subjective alignment of a velocity-encoding axis employed by a pulse sequence used for MR data acquisition, with the principle axis of the jet, and also due in part to using insufficient temporal resolution when sampling blood flow data. Manual alignment of these axes may be difficult, particularly as post-stenotic jets frequently exhibit a degree of eccentricity and can change direction throughout a cardiac cycle. Obtaining sufficiently high temporal resolution in MR image data acquisition is difficult, particularly as lower temporal resolution multi-dimensional phase-contrast pulse sequences are typically used to derive the flow information.
Known systems employ phase-contrast pulse sequences to acquire MR image data having two-dimensional spatial-encoding and three-dimensional velocity-encoding through a flow jet and perform pixel-wise root-sum-of-squares calculations to generate a two-dimensional velocity magnitude map. Visual inspection of a velocity magnitude map is used to manually guide the location, orientation, and velocity-encoding-sensitivity-factor (VENC) of a subsequent phase-contrast pulse sequence having two-dimensional spatial-encoding and single-dimensional velocity-encoding in the through-plane direction. The known systems are inaccurate for reasons including, 1) the locations and orientations of the two-dimensional slices are inaccurate due to operator dependence, 2) the VENC's of the two-dimensional slices are sub-optimal due to operator dependence, and 3) the temporal resolution of the two-dimensional slices are insufficient due to the use of multi-dimensional encoding. Known systems are time-consuming and it is often necessary to repeat image data acquisition and analysis when the operator choices are initially suboptimal. A system according to invention principles addresses these problems and related problems.